EZH2-IN-9 is a potent inhibitor of EZH2, whose overexpression or mutations in the SET region (Y641F, Y641N, A687V, A677G point mutations) cause abnormal elevations in H3K27me3 and contribute to the growth and development of many tumours (e.g. breast cancer, prostate cancer, leukaemia, etc.). EZH2-IN-9 has shown potential for cancer research.